what documentation is needed to travel to Ontario, Canada?

I want to go to Canada for a wedding in Mt.Forest, Ontario,
What do I need to cross the border into Ontario and to return to the United States

passport or birth certificate

If you are American, you will need your passport.

If you are an American citizen and want to FLY to and from Canada, you need a passport. To travel by LAND, you need a photo I.D. and a proof of citizenship...EITHER a passport OR a birth certificate. See site below for current info.

Depends on how you enter Canada.You are required to hold a valid passport if you travel by AIR. You don't need a passport when traveling by "LAND or SEA" (TILL JUNE 2009) You need a government issued photo ID such as a driver's license and birth certificate.